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AJvYcCXr9FJn1qiFxF5sxX/RgiDKHLcocP+u/S+uVkam8T8pXC0DNibXCsM0YomgWBupTWwgnAYLNExfk5aDk8PUAw==@lists.linux.dev X-Gm-Message-State: AOJu0Yz/2tnkrSLC5+wbGtfJ4TgUTJwB5fnUWr43QRe8g77C0P/WH180 bfwD36uQC4iXQReUlSxQrXNUOSk0N8BuET1FIaS1lbDORPhrbQyIehNs29iuNFOVS5ag+enzOKM GgQ== X-Google-Smtp-Source: AGHT+IFBt8EUJmCBrYJSR6SbgIXxnZj6fm10TNGjaAj4XRK+x0dRIzGirCE9VGAaKkDPtl0zEYTqCFRnILs= X-Received: from pfbcv2.prod.google.com ([2002:a05:6a00:44c2:b0:725:a760:4c72]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:148d:b0:725:eb85:f802 with SMTP id d2e1a72fcca58-72daf930e3cmr5815077b3a.2.1737134128872; Fri, 17 Jan 2025 09:15:28 -0800 (PST) Date: Fri, 17 Jan 2025 09:15:27 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250114175143.81438-1-vschneid@redhat.com> <20250114175143.81438-26-vschneid@redhat.com> Message-ID: Subject: Re: [PATCH v4 25/30] context_tracking,x86: Defer kernel text patching IPIs From: Sean Christopherson To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, x86@kernel.org, virtualization@lists.linux.dev, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-perf-users@vger.kernel.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, linux-arch@vger.kernel.org, rcu@vger.kernel.org, linux-hardening@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, Peter Zijlstra , Nicolas Saenz Julienne , Juergen Gross , Ajay Kaher , Alexey Makhalov , Russell King , Catalin Marinas , Will Deacon , Huacai Chen , WANG Xuerui , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Arnaldo Carvalho de Melo , Namhyung Kim , Mark Rutland , Alexander Shishkin , Jiri Olsa , Ian Rogers , Adrian Hunter , Kan Liang , Boris Ostrovsky , Josh Poimboeuf , Pawan Gupta , Paolo Bonzini , Andy Lutomirski , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juri Lelli , Clark Williams , Yair Podemsky , Tomas Glozar , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Kees Cook , Andrew Morton , Christoph Hellwig , Shuah Khan , Sami Tolvanen , Miguel Ojeda , Alice Ryhl , "Mike Rapoport (Microsoft)" , Samuel Holland , Rong Xu , Geert Uytterhoeven , Yosry Ahmed , "Kirill A. Shutemov" , "Masami Hiramatsu (Google)" , Jinghao Jia , Luis Chamberlain , Randy Dunlap , Tiezhu Yang Content-Type: text/plain; charset="us-ascii" On Fri, Jan 17, 2025, Valentin Schneider wrote: > On 14/01/25 13:13, Sean Christopherson wrote: > > On Tue, Jan 14, 2025, Valentin Schneider wrote: > >> +/** > >> + * is_kernel_noinstr_text - checks if the pointer address is located in the > >> + * .noinstr section > >> + * > >> + * @addr: address to check > >> + * > >> + * Returns: true if the address is located in .noinstr, false otherwise. > >> + */ > >> +static inline bool is_kernel_noinstr_text(unsigned long addr) > >> +{ > >> + return addr >= (unsigned long)__noinstr_text_start && > >> + addr < (unsigned long)__noinstr_text_end; > >> +} > > > > This doesn't do the right thing for modules, which matters because KVM can be > > built as a module on x86, and because context tracking understands transitions > > to GUEST mode, i.e. CPUs that are running in a KVM guest will be treated as not > > being in the kernel, and thus will have IPIs deferred. If KVM uses a static key > > or branch between guest_state_enter_irqoff() and guest_state_exit_irqoff(), the > > patching code won't wait for CPUs to exit guest mode, i.e. KVM could theoretically > > use the wrong static path. > > AFAICT guest_state_{enter,exit}_irqoff() are only used in noinstr functions > and thus such a static key usage should at the very least be caught and > warned about by objtool - when this isn't built as a module. That doesn't magically do the right thing though. If KVM is built as a module, is_kernel_noinstr_text() will get false negatives even for static keys/branches that are annotaed as NOINSTR.